When you’re building a robot, quadcopter or other project and object avoidance or distance sensing is imperative to your success, finding the right sensor can be a bit tricky. Today, we want to share a brilliant new sensor from the folks over at Pulsed Light - the LIDAR-Lite.

The LIDAR-Lite is a high-performance distance sensor that costs a fraction of what a sensor with comparable performance would usually cost.

This sensor has a range of 40 meters and uses some very clever innovations to attempt to imitate the performance of much more expensive"Time of Flight" distance sensors. The LIDAR-Lite uses an I2C communications interface, which allows multiple modules to be connected as slaves to a common communications bus. Plus, it draws only 100 milliamps peak power when taking a measurement and under 10 milliamps when idle, making the LIDAR-Lite a great option when power consumption is a concern.

Check out their crowdfunding campaign for more information on the tech behind the LIDAR-Lite and to purchase your own!

I have the following questions before considering buying the sensor.
What is your rms accuracy and range at maximum sampling rate (I assume 100Hz)?
What is the target you use when you make all your distance claims?
Why have you not placed your 1" optics on the receiver and done some tests, are you worried about saturation of the sensor from ambient light or increased noise?

Sorry for the delay in responding! You’ve asked good questions. First let me refer you to our YouTube technical presentation where the engineer behind LIDAR-Lite, Bob Lewis, spent over an hour discussing our technology and answering questions live - including ones very similar to those you just asked. I think you’d find it very interesting. The link is https://www.youtube.com/watch?v=K5bUvomrQkQ .

The short answers to your questions are;
The rep rate is dynamically adjustable between 1 and 100Hz. Up to 10Hz the maximum range would be 40m against a 90% target. As the rep rate increases the maximum distance will decrease until at 100Hz it’s approximately 20m.

We haven’t tested with the production optics simply because we haven’t received them yet from our supplier. We have done testing with smaller, off-the-shelf optics, which were less than perfect, but based on those results the math tells us that we will reach our performance goals when we do get our production optical components which are specifically designed for this sensor.

We have an IR filter on the detector which makes is pretty immune to solar gain, other than directly looking into the sun. Ambient light is not going to be a significant issue since our signal processing has been designed to operate effectively in the noise. We’ve even tested looking directly at a florescent light with not effect on performance.

I hope you enjoy the video. If you have any additional questions, please let us know either through this blog or you can ask directly through our website at www.pulsedlight3d.com .

Thank you for your explanation. I did look at your video and still did not get the answer I was looking for. Could you please set up your device without any additional optics in front of a 90% target at 5m and provide the standard deviation of the readings (20 readings) and please provide the sampling rate used. I hope this clarifies what I am looking for. Thank you again for all the feedback.

We’ll be very happy to share with you the results of our testing of the sensor when we have reached the final iteration of our design. Until then it would be counterproductive to release test data that wasn’t entirely accurate or representative of the final product. We are currently working on code and hardware updates from our first prototype build and have a second build of prototypes in process. Our goal is to be ready to go to production as soon as possible after reaching our funding goals so that we are not keeping our backers waiting any longer than necessary. As soon as the final test data becomes available we will publish it.

It sounds like you may have a very specific application in mind for our sensor and we’d be very happy to speak with you directly about your requirements. It might be more efficient in the long run in addressing your questions. You can reach us directly via email at sensors@pulsedlight3d.com to arrange a call. We look forward to talking with you and having you become a backer.

How many measurements can I take per second? I sent this question in on the crowdfunding ‘ask us’ link and never got an answer. I’m not too keen on investing in a product where the company who wants my money won’t answer basic questions.

There was a discussion of this topic on our crowdfunding site, but I apologize if your specific question was overlooked. It certainly wasn’t intentional!

To further elaborate on Mike’s comments, the rep rate is dynamically configurable from 1 to 100hz, but at the maximum rate the range is reduced by 50%. This is because of the amount of time the system has for each measurement at that rep rate.

It sounds like they are using phase difference of arrival to measure time of flight? It was hard to tell in the video, the guy was very vague about the technology, at least the way they edited the video (it seems like part of the explanation got edited out).

We are actually using a combination of time-of-flight and correlative signal processing (similar to what is used radar) as the basis of our signal processing technology. I would encourage you to join us next Tuesday when we host a G+ Hangout to discuss our technology and answer questions. More information about the event is available at https://plus.google.com/u/0/events/c8m5nu1uerpgofbbb7o3k1ck2lk

How does the unit perform in bright sunlight conditions? What about in the presence of external light sources such as street lamps? Yes they are transmitting coded messages and doing synchronous detection but one still has to be concerned about saturating the amplifier from external CW sources.

The data sheet quotes a maximum range distance of 5 meters without optics and 40 meters with. What is the average optical power incident on the photodiode for reflection off a white surface. This matters because there doesn’t appear to be any gain control. If the gain is fixed so that small distances don’t saturate the amplifier then the signal to noise ratio at this distance will be very poor.

How does this compare to a conventional ultrasonic based sensor such as the line of Maxbotix sensors sold at sparkfun. The LIDAR-lite data sheet quotes an absolute accuracy of 5% presumably across the entire 0 to 5 meter range. No absolute accuracy is provided from Maxbotix but if you look at this link:
http://www.maxbotix.com/articles/057.htm

The worst case for a 500mm test was 494mm with a given sensor so a worst case accuracy of 1.2%. Maxbotix quotes a standard deviation of 2.3mm and 2.6mm for distances of 500mm and 1m respectively. LIDAR-lite doesn’t provide this specification which is a bummer as this is the real defining performance specification.

These are all great questions that have, at least in part, been answered in a variety of forums ranging from Reddit to Hackaday to our crowdfunding site’s Q&A section. As is mentioned below by Emcee Grady, I would really encourage you to take part in the hangout on the 26th.

To directly and VERY briefly answer your questions;
1. Since we can operate well below the noise level, sunlight is not a significant issue, but it can be an issue nontheless.
2. Yes. However, we are using processing gain to pull the signal out of the noise at longer distances not amplifier gain, as a result at shorter distances we are not saturating the amplifier. So our signal processing is, in effect, our AGC. (That was the VERY short answer!)
3. Our logic chip’s internal clock has a reported 5% accuracy, so we didn’t want make any claim of greater accuracy. Our experience so far is that the clock is about 1% accurate and we have also made provision on the board for the connection of an external reference so that the user can realize a 1cm accuracy across the full operating range of the sensor.

You’ve asked some great questions and I would, again, suggest that you attend our G+ Hangout.

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